Thick film dielectric structures are typically fabricated on ceramic substrates and provide superior resistance to dielectric breakdown, as well as a reduced operating voltage compared to thin film electroluminescent (TFEL) displays fabricated on glass substrates. When deposited on a ceramic substrate, the thick film dielectric structure withstands higher processing temperatures than TFEL devices on glass substrates. The increased tolerance to higher temperatures facilitates annealing of the phosphor films at higher temperatures to improve luminosity. However, even with the enhanced luminosity that is obtained, it is desirable to further increase the luminous efficiency of the devices to enable an improvement in overall energy efficiency and reduction in power consumption.
The Applicant has developed various methods for the deposition of phosphors used in thick film dielectric electroluminescent devices that are described for example in U.S. Pat. No. 5,432,015 (the entirety of which is incorporated herein by reference in its entirety). For example, International Patent Application PCT CA01/01823 (the disclosure of which is incorporated herein in its entirety) a method of electron beam vaporization for the deposition of a ternary, quaternary or similar phosphor composition, in which components of the composition are located on different sources. In particular, the compositions are thioaluminates, thiogallates or thioindates of Group IIA and Group IIB elements, and the sulfides that form such compounds are located on the different sources. The Applicant's International Patent Application PCT CA01/01234 (the disclosure of which is incorporated herein in its entirety) discloses a dual source phosphor deposition method using dual source electron beam deposition. The various compounds of the first and second sources are in the ratios required to provide the required composition of the phosphor. The deposited phosphors are preferably blue emitting europium activated barium thioaluminate (BaAl2S4:Eu). The Applicant's International Patent Application PCT CA02/00688 (the disclosure of which is incorporated herein in its entirety) discloses a single-source sputtering method for depositing controlled composition multi-element phosphor films. The method utilizes a source material in the form of a single dense target that has a composition different from the desired film composition of the phosphor. The concentrations of light chemical elements relative to heavier chemical elements in the target composition of the process is higher than desired in the deposited films.
In the deposition of phosphor compositions, it would be desirable to remove undesired chemical species from the deposition atmosphere in order to minimize the risk of such undesired chemical species from being incorporated into the deposited phosphor film. Getters are known materials that getter reactive gases in a variety of applications as is described for example in U.S. Pat. Nos. 4,062,319, 4,118,542, 5,508,586, 6,514,430 and 6,586,878.
U.S. Pat. No. 5,976,900 describes a pre-coat layer provided on interior surfaces of a process chamber that acts as a getter to mobile ions. The pre-coat layer is applied to the surfaces of the process chamber prior to any wafer processing.
U.S. Pat. No. 6,299,746 describes a getter system for purifying a gaseous atmosphere within a process chamber. The getter system comprises a planar getter device disposed within the process chamber.
U.S. Pat. No. 6,299,689 describes the use of a gettering material within a reflow chamber containing a shield that prevents the gettering material from reaching the material layer to be reflowed.
While the aforementioned patents disclose the use of getter materials, it is desirable to provide an improved method for gettering undesirable atomic species during deposition of phosphor compositions for use in thick film dielectric electroluminescent displays in order to further improve luminance and luminous efficiency of the phosphor compositions.